This invention relates to a digital circuit arrangement for detecting horizontal or vertical synchronising pulses in a digital video signal.
Known circuit arrangements for separating horizontal or vertical synchronising pulses from video signals use a separating circuit for the horizontal or vertical synchronising pulses and compare them with a clipping level obtained from the pulse amplitude. This clipping level is, however, always an average amplitude of the television signal, no matter what criteria are used. As a result, considerable problems arise in disturbed input signals (large noise component) in which the synchronising pulses can no longer be recognized unambiguously.
European Patent Application 244,239 discloses a separating circuit for synchronising pulses in which the edges of the synchronising pulses are detected. The signal then obtained is utilized to generate a clipping level. To detect the edges of the pulses in the video signal, assumptions about their edge steepness are required. If these criteria are no longer achieved, as is the case, for example, in a disturbed signal, either no synchronising pulse is detected or it may lead to erroneous detections.